Drum brakes are a type of braking system that uses friction to slow the rotation of a drum. In a common application, drum brakes are used to reduce the rotational speed of a drum coupled to a vehicle wheel in order to slow the vehicle, to bring the vehicle to a stop, and to ensure the vehicle remains stationary. Generally, drum braking systems include a drum, brake shoes, a backing plate, and a hydraulic cylinder. The drum is a cup-shaped structure that is coupled to an axle. In particular, the drum is often coupled between a wheel and a wheel end of the axle for rotation with the wheel and the axle. The interior of the drum includes a cylindrical surface, referred to as the braking surface. The brake shoes contact the braking surface when the drum braking system is activated. The backing plate is a generally disc-shaped element having a diameter similar to the diameter of the drum. In most configurations, the backing plate is fixed to an axle support structure located near the wheel end of the axle. The backing plate does not rotate with the wheel, drum, and axle; instead, a wheel side of the backing plate supports the hydraulic cylinder, the brake shoes, and the other braking components.
The hydraulic cylinder forcibly pivots the brake shoes against the braking surface of the drum to stop or to limit the rotation of the drum. The hydraulic cylinder includes two pistons that slide in a bore and that define a sealed chamber between them. An end of each piston contacts one of the brake shoes, which are pivotally coupled to the backing plate.
To activate the drum braking system an actuator, usually a foot pedal, is moved, thereby causing an increased hydraulic pressure in the sealed chamber of the hydraulic cylinder. The increased pressure forces the pistons to extend from the bore and to pivot the brake shoes into contact with the braking surface of the drum. Friction between the brake shoes and the braking surface slows the rotation of the drum and the rotation of a corresponding wheel coupled thereto.
In addition to being hydraulically activated, a drum braking system may also include a mechanical actuation system that provides a parking brake or an emergency brake function. The mechanical actuation system is operable to pivot at least one of the brake shoes into contact with the braking surface of the drum, even when the hydraulic cylinder is inactivated, disabled, or nonfunctional. The mechanical actuation system may include a brake lever, a hand or foot operated actuator (referred to as a manual actuator), and a cable. The brake lever is pivotally connected to the wheel side of the backing plate. As the brake lever is pivoted in a braking direction, one or more of the brake shoes are forced into contact with the braking surface of the drum. Likewise, as the brake lever is pivoted in a release direction, the brake shoes pivot away from the braking surface of the drum. The cable couples the brake lever to the manual actuator, which is movable between an engaged and a disengaged position. When the manual actuator is moved to the engaged position, the cable applies a force to the brake lever thereby causing it to pivot in the braking direction, and, in turn, causing the brake shoes to pivot toward and contact the braking surface, thereby reducing the rotational speed of the drum. Similarly, movement of the manual actuator to the disengaged position causes the brake lever to pivot in the release direction, and, in turn, reducing or eliminating the force maintaining the brake shoes against the braking surface of the drum and enabling the drum to rotate freely.
It can be time consuming and cumbersome to connect the cable to the brake lever of some drum braking systems. Specifically, due to the cup shape of the drum and the generally disc shape of the backing plate, the brake lever becomes concealed when the drum is coupled to the axle. Therefore, further developments in the area of brake levers for drum braking systems are desirable.